A corrupted file has been blamed for a glitch on the Federal Aviation Administration’s computer system which saw every flight grounded across the US.

All outbound flights were grounded until around 9am Eastern Time (2pm GMT) on Wednesday as the FAA worked to restore its Notice to Air Missions (NOTAM) system, which alerts pilots of potential hazards along a flight route.

As of 3pm GMT yesterday 4,948 flights within, into or out of the US had been delayed, according to flight tracker FlightAware.com, while 868 had been cancelled. Most delays were concentrated along the East Coast.

Normal air traffic operations resumed gradually across the US following the outage to the NOTAM system that provides safety information to flight crews.

A corrupted file affected both the primary and the backup systems, a senior government official told NBC News on Wednesday night, adding that officials continue to investigate.

“We are continuing a thorough review to determine the root cause of the Notice to Air Missions (NOTAM) system outage” the FAA said in an update yesterday.

“Our preliminary work has traced the outage to a damaged database file. At this time, there is no evidence of a cyberattack.”

It added work was ongoing to “further pinpoint the causes of this issue” and take “all needed steps to prevent this kind of disruption from happening again”.

‘Almighty mess’

Sky News correspondent Mark Stone, who was at Ronald Reagan Airport in Virginia, said at the time of the outage: “Well an almighty mess for the aviation industry in the United States.

“We were told that the NOTAM system had failed, which is part of the air traffic control system. This is critical for flights to be able to take off safely. So as a consequence the busiest airspace in the world, the airspace over the United States, didn’t open as it should have done.

“Looking at the flight tracker websites it was very clear you could see flights clustered around many cities around the United States and none of them taking off. Chaos for passengers, as you might imagine.”

No evidence of cyberattack

US President Joe Biden was briefed on the outage, his press secretary Karine Jean-Pierre said.

She said there was no evidence a cyberattack was behind the glitch, “but the president directed [the US Department of Transport] to conduct a full investigation into the causes”.

Mr Biden told reporters during the outage yesterday: “They don’t know what the cause of it is, they expect in a couple of hours they’ll have a good sense of what caused it and will respond at that time.”

The president added that he had spoken to Transportation Secretary Pete Buttigieg on the phone, and told him “to report directly to me when they find out”.

Several people tweeted to say they had been stranded due to the outage, with one passenger at Paris’ Charles de Gaulle airport saying no flights were flying to the US.

A total of 21,464 flights were scheduled to depart airports in the US today, according to aviation analytics firm Cirium.

Nearly 2.9 million seats are available on those departures.